Calcium soap grease containing lithium hydroxide



- 2,967,826 CALCIUM SOAP GREASE CONTAINING LITHIUTVI HYBROXEE John P. Dilworth, Fishkill, Bill L. Benge, Clinton Hollow, and Terence B. Jordan, Fishkill, N.Y., assignors to Texaco Inc., a corporation of Delaware No Drawing. Filed Dec. 23, 1957, Ser. No. 704,290 17 Claims. (Cl. 252-18) This invention relates to improved lubricating greases and to a method of preparing them. More particularly, it relates to anhydrous calcium base greases containing a small amount of free lithium hydroxide, prepared by a method which comprises a high temperature digestion step.

We have found that anhydrous calcium base greases characterized be very high dropping points and other superior lubricating properties are obtained in high yields by the method which comprises a high temperature digestion step carried out upon a dehydrated mixture of calcium fatty acid soap and mineral lubricating oil containing lithium hydroxide in the calculated amount to give about l-3 percent by Weight of freelithium hydroxide in the finished grease. By this method, anhydrous calcium base greases are obtained having dropping points above 400 F, or very much higher than those obtainable in the conventional calcium base greases. Under the preferred con ditions, anhydrous calcium base greases having dropping points up to 500 F. or even higher are obtainable by the method of this invention.

The calcium soaps which are employed as thickening agents in these greases may be obtained from any of the saponifiable materials commonly employed in grease making, comprising higher fatty acids, containing at least 12 carbon atoms per molecule, which may be saturated, unsaturated or hydroxy substituted fatty acids, or the glycerides or other esters of such acids or mixtures of free fatty acids and their esters. The preferred saponifiable materials are those which comprise at least a major portion of fatty acids containing from about 14 to 22 carbon atoms per molecule, such as for example, myristic acid, palmitic acid, stearic acid, oleic acid, tallow fatty acids, IZ-hydroxystearic acid, 9,10-dihydroxystearic acid, etc., or the glycerides or other esters of such acids.- Very advantageously, a fatty acid material comprising about 20-50 percent of fatty acids containing more than 18 car bon atoms per molecule or their glycerides or other esters may be employed for this purpose. Suitable fatty acid materials of this character include particularly the fish oils and fish oil fatty acids, which may be hydrogenated to reduce their unsaturation. Especially suitable materials of this character comprise at least about 20 percent by Weight of fish oil, having an iodine number of about 100-200, which may be employed in admixture with saturated or substantially saturated fatty acid materials such as myristic acid, stearic acid, tallow fatty acids, l2-hydroxystearic acid, etc.

In accordance with the preferred embodiment of this invention, the calcium soap is derived from a saponifiable material which contains a substantial proportion of unsaturated fatty acid material, such that the saponifiable material has an iodine number of at least about 40, most suitably from about 40 to about 100, and also comprises at least about 20 percent by Weight of hydroxy fatty acid material. An unsaturated hydroxy fatty acid material is very advantageously employed, either alone or in admixture-with other fatty acid materials, which may be saturated or unsaturated and/ or hydroxy substituted fatty acid materials, or mixtures thereof. A very suitable unsaturated hydroxy fatty acid material for this purpose is castor oil, comprising chiefly glyceryl ricinoleate. A particularly preferred saponifiable material comprises a mixture nite States Patent O F of castor oil with both unhydrogenated fish oil and with a substantially saturated fatty acid material, wherein the proportions of the different saponifiable materials are in about the range 0.5-2 with respect to each other. The saturated fatty acid material is very suitably a fatty acid mixture derived from the hydrogenation of fish oil fatty acids. Such a material is known commercially as Snodotte acids, and comprises about 9 percent myristic acid, about 22 percent palmitic acid, about 27 percent stearic acid, about 22 percent 'arachidic acid and about 20 percent behenic acid.

The greases of this invention comprise essentially a mineral lubricating oil thickened to a grease consistency with a calcium fatty acid soap of the character described above and containing a small amount of free lithium hydroxide. In general, the proportion of calcium fatty acid soap may be from about 5 to about 45 percent by weight of the grease composition, and preferably from about 10 to about 30 percent by weight of the composition.

The lubricating oil component of these greases is preferably a naphthene base oil or a mixture of lubricating oils comprising naphthene base oils in major proportion. The oils may be either distillate or residual fractions obtained by any of the conventional refining processes, having viscosities in the usual lubricating oil viscosity range. Preferably, the lubricating oil component has a viscosity in the range from about 300 seconds Saybolt Universal at F. to about 100 seconds Saybolt Universal at 210 R, which may be obtained by blending oils of higher and lower viscosities within the lubricating oil range.

Additives of the usual types may be employed in these greases, such as extreme pressure agents, pour depressants, oxidation inhibitors, corrosion inhibitors, dyes, and the like. Very suitable oxidation inhibitors are those of the amine type, such as diphenylamine, alphaand betanaphthylamines and N,N' diphenyl-para-phenylenediamine. A compound of this type may be employed suitably in an amount from about 0.5 to about 3 percent by Weight, based on the weight of the grease. Very advantageously, about 1-10 percent by Weight of aluminum stearate may be added to these greases in order to impart improved water resistance. Minor amounts of additional thickening agents such as other soaps, polymeric materials, or finely divided solids of various types may also be added.

The preferred method of grease preparation comprises saponifying the fatty acid material in situ in a portion of the lubricating oil contained in the grease, such as about one-fourth to one-half of the total lubricating oil component, dehydrating, adding the remainder of the mineral lubricating oil, and then carrying out the high temperature digestion step upon the grease mixture to which lithium hydroxide has been added. The saponification is suitably carried out at a temperature in about the range ISO-225 F., and the dehydration at a higher temperature, suitably in about the range 250350 F. The saponification may be carried out employing the theoretical amount of lime required to react with the fatty acid material, or a small excess may be employed if desired, sufiicient to give a calculated free calcium hydroxide content of about 0.05- 0.5 percent to the finished grease. The lithium hydroxide may be added to the saponification mass together with the lime or it may be added at any time prior to the high temperature digestion step. It is preferably added following the saponification and prior to the dehydration step.

The high temperature digestion step is carried out in the presence of oxygen at a temperature in about the temperature in about the range 450-550 F., and most Patented Jan. 10, 1961 advantageously at a temperature in about the range 480-550 F., for about2-4 hours. This high temperature digestion step produces a very marked increase in both the dropping point and'the yield, as well as improvements in other lubricating properties, including particularly improved texture and shear stability. The reactions occurring whereby these effects are produced are not entirely understood, although it is assumed that they involve oxidation reactions of some sort. It does not appear that any substantial amounts of lower fatty acid soaps are formed in the reactions, since usually no more than a slight decrease in free alkali content is observed. Under the preferred conditions, for example, employing 1-2 percent by weight of lithium hydroxide, the free alkali content of the finished grease will usually be in about the range 0.6-1.8 percent by weight, based on the weight of the finished grease.

By the term "free alkali as employed herein is meant alkali which is readily titratable, as for example under the conditions of the standard ASTM titration method. Such alkali is commonly spoken of as free alkali, although it is not known whether it is actually present in the uncombined state or combined in some readily hydrolyzable form.

Following the high temperature digestion, the grease mixture is cooled with stirring to the drawing temperature, which may be about 200 F. or somewhat lower. Various additives may be blended into the grease during the cooling at a suitably low temperature, usually below about 250 F. When aluminum stearate is added to the grease it is preferably added while the grease mixture is still at an elevated temperature, such as about 400-500 F. Milling of the grease mixture may be employed in order to improve the grease texture and yield. The milling may be carried out upon the drawn grease by any of the conventional methods, or it may be carried out during the cooling by the method of J. P. Dilworth, T. B. Jordan and B. L. Benge, as described in their copending application Serial No..5l3,282, filed June 6, 1955, now US Patent No. 2,886,525. As described therein, the grease mixture is subjected to shearing during cooling by a recycle method wherein the recycle stream is passed through a shear valve with a pressure drop of about -200 pounds per square inch, and preferably with a pressure drop of about 25-75 pounds per square inch across the valve. The recycling is carried out at a rate such as to give at least one complete batch turnover while the grease is cooled from a temperature above its melting point, and ordinarily at least about five batch turnovers in the range from the melting point of the grease down to about 200 F.

The following examples are given for the purpose of further disclosing the invention.

Example I A grease representative of the greases of this inventron was prepared having the following calculated composition in percent by weight:

Calcium myristate 10 Excess Ca(OH) 0.2 Excess LiOH 1.5 Mineral lubricating oil Remainder The mineral lubricating oil employed in the grease was a blend in a 35:65 proportion by weight of a refined naphthene base distillate oil having a Saybolt Universal viscosity at 100 F. of about 100 seconds and a naphthene base residual oil having a Saybolt Universal viscosity at 210 F. of about 200 seconds.

The grease preparation was carried out in the following manner: A mixture of 19.0 pounds of the mineral lubricating oil, 5.45 pounds of myristic acid, and an aqueous slurry of 1.1 pounds of lime were charged to a fire-heated open grease kettle and heated at about 180- 200 for two hours. Following the saponification,

380 grams of lithium hydroxide were added, and the temperature of the mixture increased to 300-325" F. to dehydrate. After one hour the temperature was further increased to about 450 F. and an additional 34.0 pounds of lubricating oil-were added gradually during about 30 minutes while the temperature was maintained at about 450 F. The mixture was then further heated to 500 F. in about 30 minutes. The heat was then shut off and the mixture was cooled at an average rate of about 2 F. per minute by continuously withdrawing a minor recycle stream from a maintained body of the grease m xture and passing it through an outside cooler at a recycle rate of 78 pounds per minute while the grease was cooled from about 500 F. down to about 200 F. The grease was subjected to shearing during the cooling by passing the recycle stream through a gate valve in the cooler line with a pressure drop of 75 pounds per square inch across the valve. The grease was finally drawn at F.

A black, somewhat rough textured grease was obtained by the above method, having the following properties:

ASTM penetration at 77 F Unworked 168 Worked (60 strokes) 228 Dropping point, F. 416

Free fatty acid, percent None Free alkali, percent 1.4

The above tests were carried out by the standard ASTM procedures, except for minor modifications in the free alkali determination. These comprised employing a benzeneisopropyl alcohol mixture as the solvent instead of a naphtha-ethyl alcohol mixture, and titrating with 0.1 N KOH instead of 0.5 N KOH.

As shown by the above data, a grease having a very high dropping point for a calcium base grease was obtained and in very good yield by employing the method of this invention. In contrast to this result, only liquid products were obtained by carrying out the procedure in the same manner upon a grease mixture of the same composition except that it contained no lithium hydroxide.

Example 11 A grease representative of the preferred greases of this invention was prepared having the following calculated composition in percent by weight:

ployed in the grease preparation described in Example I.

The method of preparation was substantially the same as that employed in Example I, except that the sap0nifiable material employed was a commercial castor oil having a saponification number of 176, a neutralization number of 1.9, an iodine number of 64 and a hydroxyl number of 156, and the grease mixture was held at 500 F. for 3 hours following the dehydration. About 6 grams of methyl silicone (Dow Corning Antifoam A) were added to the saponification mixture, amounting to 0.02 part per million of the finished grease.

A soft black grease of good texture was obtained by the above method, having the following properties:

ASTM penetration at 77 F.:

Unworked 358 Worked (60 strokes) 384 Dropping point, F 500+ Free fatty acid, percent None Free alkali, percent 1.5

aeeaeze The above tests were carried out as described in Example I.

In contrast to the result obtained as described above, attempts to prepare greases of the same composition without the lithium hydroxide were unsuccessful, only liquid products being obtained with grease mixtures containing no alkali metal hydroxide and also with those containing 1.5 percent sodium hydroxide in place of the lithium hydroxide.

Example III A grease representative of the particularly preferred embodiment of this invention was prepared having the following calculated composition in percent by weight:

Calcium soap of castor oil 3.3 Calcium soap of menhaden oil 3.3 Calcium soap of Snodotte Acids 3.4 Excess Ca(OI-I) 0.2 Excess LiOH 1.5 Glycerine 0.7 Aluminum stearate 2.5 Mineral lubricating oil Remainder The mineral lubricating oil was the same as that employed in the grease preparation described in Example I. The saponifiable material was a mixture in the indicated proportions of the-following: Commercial castor oil; commercial menhaden oil, having a saponification number of 205, a neutralization number of 3.2, an iodine number of 167 and a titer, C., of 29.5; and Snodotte Acids, having saponification and neutralization numbers of 190-195, an iodine number of 1.5 and a titer, C., of 58.1.

The grease preparation was carried out substantially as described in Example II, employing a small amount of methyl silicone, equivalent to 0.2 part per million of the finished grease, in the saponification mixture. The aluminum stearate was added to the mixture following the high temperature digestion step while the mixture was at about 500 F.

A black grease of satisfactory texture was obtained having very superior lubricating properties as shown by the following table. The table also shows the properties of a grease of the same composition prepared by the same method except that the high temperature digestion step was omitted (A), and those of a grease prepared in the same manner as the grease of Example III and of the same composition except that 1.5 percent NaOH was employed instead of the LIOH(B). In the preparation of Grease A, the grease mixture was heated to 400 F. following the dehydration and cooled with no holding at that temperature.

Grease Ex. III A B ASTM Penetration at 77 F.:

Unworked 222 0 161. Worked (60 strokes) 253 96 233. Worked (100,000 strokes) 290 Too soft for penetration Dropping Point, F 500+ 345 358. Free fatty acid, percent None 0.5. Free alkali, percent 1.2 1.2. Dynamic Water Resistance, per- 2.5

cent less. Shell Roll Test, Penetration after 242 Too soft test. for penetration. Texture Satisfac- Tacky Stickytory. slightly rubbery.

As shown by the data given in the above table, the high dropping points and other superior grease properties obtained in the greases of this invention are critically dependent upon both the high temperature digestion treatment and also upon the particular alkali metal hydroxide employed, the use of sodium hydroxide as the excess alkali resulting in low dropping point greases of rubberyvention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof and therefore, only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. In the preparation of calcium base greases, the improvement which comprises heating a dehydrated mixture of a calcium fatty acid soap and mineral lubricating oil containing about l-3 percent by weight based on the weight of the finished grease of lithium hydroxide at a temperature in about the range 400600 F. for about 1-5 hours in the presence of oxygen until a product having an ASTM dropping point above 400 F. is obtained, containing free alkali in an amount equivalent to at least about 60 percent by weight of the lithium hydroxide originally present in the said mixture.

2. The method according to claim 1 wherein the said mixture is heated at a temperature in about the range 450-550" C. for about 2-4 hours at substantially atmospheric pressure.

3. The method according to claim 1 wherein the said mineral oil is a naphthene base oil.

4. The method according to claim 1 wherein the said calcium fatty acid soap is the calcium soap of a sapom'fiable material having an iodine number of at least about 40 and comprising at least about 20 percent by weight of hydroxy fatty acid material.

5. The method according to claim 1 wherein the said calcium fatty acid soap comprises at least about 20 percent by weight of a calcium soap of an unsaturated hydroxy fatty acid material.

6. A process for preparing calcium base greases which comprises saponifying a fatty acid material with lime in the presence of a naphthene base lubricating oil constituting about flt- /z of the total oleaginous component of the finished grease, thereafter adding lithium hydroxide in an amount equal to about l-3 percent by weight of the finished grease, dehydrating, adding the remainder of the lubricating oil contained in the grease, heating the grease mixture thus obtained at 480550 F. for about 2-4 hours at substantially atmospheric pressure in the presence of oxygen until a grease having a dropping point above 400 F. is obtained, containing free alkali in an amount equivalent to at least about 60 percent by weight of the lithium hydroxide originally present in the said mixture, and finally cooling the grease mixture with stirring to the drawing temperature.

7. The method according to claim 6 wherein the grease mixture is subjected to shearing during the said cooling by recycling it through a shear valve with a pressure drop across the said valve of about 10-200 pounds per square inch, said recycling being carried out at a rate such as to give at least one complete batch turnover during the said cooling.

8. A lubricating grease comprising a mineral lubricating oil thickened to a grease consistency with about 545 percent by weight of a calcium fatty acid soap and con taining at least about 0.6 percent by weight of free lithium hydroxide, said grease being prepared by a method which comprises the step of heating a dehydrated mixture of calcium fatty acid soap and mineral lubricating-oil containing about 1-3 percent by weight of lithium hydroxide based on the weight of the finished grease at a temperature in about the range 400-600 F. for about 1-5 hours in the presence of oxygen until a product having an ASTM dropping point above 400 F. is obtained, containing free alkali in an amount equivalent to at least about 60 percent by weight of the lithium hydroxide originally present in the said mixture.

9. A lubricating grease according to claim 8 wherein the said heating step is carried out at a temperature in c em-2e 7 about the range 450550 F. and at substantially atmospheric pressure for 2-4 hours.

10. A lubricating grease comprising a mineral lubricating oil thickened to a grease consistency with about 10-30 percent by weight of a calcium soap and containing at least about 0.6 percent by weight of free lithium hydroxide, said grease being prepared by a method which comprises the step of heating a dehydrated mixture of calcium fatty acid soap and a naphthene base lubricating oil containing about 1-3 percent by weight of lithium hydroxide based on the weight of the finished grease at about 480-550 F. in the presence of oxygen and at substantially atmospheric pressure for about 2-4 hours until a product having an ASTM dropping point above 400 F. is obtained, containing free alkali in an amount equivalent to at least about 60 percent by weight of the lithium hydroxide originally present in the said mixture.

11. A lubricating grease according to claim 10 wherein the said calcium fatty acid soap is obtained by saponifying a fatty acid material having an iodine number of at least about 40.

12. A lubricating grease according to claim 11 wherein the said fatty acid material comprises at least about 20 percent by weight of hydroxy fatty acid material.

13. A lubricating grease according to claim 11 wherein the said fatty acid material comprises about 20-50 percent by weight of a fatty acid material selected from the group consisting of fatty acids containing more than 18 carbon atoms per molecule, the glycerides of such acids and mixtures of the acids and their glycerides.

14. A lubricating grease according to claim 11 wherein the said fatty acid material comprises at least about 20 percent by Weight of an unsaturated hydroxy fatty acid material.

15. A lubricating grease according to claim 11 wherein the said fatty acid material comprises a mixture of castor oil, hydrogenated fish fatty acids and unhydrogenated fish oil in a ratio of about 0.52:0.5-2:0.5-2 by weight.

16. A lubricating grease according to claim 10 containing about 0.05-0.5 percent by weight of free calcium hydroxide.

17. A lubricating grease according to claim 10 containing about 11() percent by weight of aluminum stearate.

References Cited in the file of this patent UNITED STATES PATENTS 2,417,429 McLennan Mar. 18, 1947 2,684,944 Zajac July 27, 1954 2,755,247 Dilworth et al. July 17, 1956 2,755,256 Dilworth et al. July 17, 1956 2,831,812 Worth Apr. 22, 1958 FOREIGN PATENTS 736,921 Great Britain Sept. 14, 1955 

1. IN THE PREPARATION OF CALCIUM BASE GREASES, THE IMPROVEMENT WHICH COMPRISES HEATING A DEHYDRATED MIXTURE OF A CALCIUM FATTY ACID SOAP AND MINERAL LUBRICATING OIL CONTAINING ABOUT 1-3 PERCENT BY WEIGHT BASED ON THE WEIGHT OF THE FINISHED GREASE OF LITHIUM HYDROXIDE AT A TEMPERATURE IN ABOUT THE RANGE 400-600*F. FOR ABOUT 1-5 HOURS IN THE PRESENCE OF OXYGEN UNTIL A PRODUCT HAVING AS ASTM DROPPING POINT ABOVE 400*F. IS OBTAINED, CONTAINING FREE ALKALI IN AN AMOUNT EQUIVALENT TO AT LEAST ABOUT 60 PERCENT BY WEIGHT OF THE LITHIUM HYDROXIDE ORIGINALLY PRESENT IN THE SAID MIXTURE. 